https://doc.rust-lang.org/stable/nightly-rustc/rustc_trait_selection/infer/canonical/ir/struct.ProjectionPredicate.html
ProjectionPredicate in rustc_trait_selection::infer::canonical::ir - Rust
This kind of predicate has no direct correspondent in the syntax, but it roughly corresponds to the syntactic forms:
traitselectioninfercanonicalir